Prism, Imaging Device and Lighting Device Including the Same, and Prism Manufacturing Method

ABSTRACT

A prism  30  includes a prism body  30 . The prism body  31  is formed into a polygonal column. At least one of a plurality of ridges  35, 36  of the prism body  31  is formed into an R-plane.

TECHNICAL FIELD

In recent years, prisms are widely used as essential parts of various kinds of optical equipment, such as DSCs (digital still cameras), DVCs (digital video cameras), cameras for mobile phones, projection televisions, and the like, and the range of uses thereof is expanding. While, demands for higher precision, compaction, and weight reduction of the various optical equipment are increasing. In association therewith, the prisms used in the various optical equipment are required to have higher performance, such as higher precision, higher functionality, higher strength, and the like.

A general triangular prism includes three side faces as optical function planes and two end faces as non-optical function planes. As a glass-made prism manufacturing method, a generally-called press molding method is known in which a material to be molded is heated and pressed and then is cooled (see, for example, Patent Document 1).

When a prism is molded by the press molding method disclosed in Patent Document 1, each ridge where the planes are intersected with one another is formed sharply. Accordingly, in handling the prism, specifically, in conveyance, in mounting to optical equipment, and the like, the ridges may be broken or chipped by external impact. For this reason, desired prism performance cannot be obtained, and the yield of the optical equipment lowers.

For tackling the above problems, namely, for suppressing breakage and chipping of the ridges, a prism of which ridges are chamfered after press molding has been proposed (see, for example, Patent Document 2):

Patent Document 1: Japanese Patent Application Laid Open Publication No. 7-69651A Patent Document 2: Japanese Patent Application Laid Open Publication No. 6-103101A SUMMARY OF THE INVENTION Problems that the Invention is to Solve

In Patent Document 2, however, a post treatment is added after prism molding, increasing the number of processing steps and costs. Further, the ridges of the prism before the post treatment are sharp yet, still remaining the problems of breakage and chipping.

The present invention has been made in view of the foregoing and has its object of providing a prism of which breakage and chipping hardly occur.

Means for Solving the Problems

A prism according to the present invention includes: a prism body formed into a polygonal column. At least one of a plurality of ridges of the prism body is formed into an R-plane.

An imaging device according to the present invention includes: a light receiving element; and a prism. The prism includes a prism body formed into a polygonal column. At least one of a plurality of ridges of the prism body is formed into an R-plane. The prism body is in a form of a right triangular prism including two orthogonal side faces which are intersected at a right angle with each other and an inclined side face which is inclined with respect to the two orthogonal side faces. The prism body is arranged so that incident light to the prism body is reflected by the inclined side face toward the light receiving element.

A lighting device according to the present invention includes: a light source; and a prism. The prism includes a prism body formed into a polygonal column. At least one of a plurality of ridges of the prism body is formed into an R-plane. The prism body is in a form of a right triangular prism including two orthogonal side faces which are intersected at a right angle with each other and an inclined side face which is inclined with respect to the two orthogonal side faces. The prism body is arranged so that light from the light source is reflected by the inclined side face.

In a first prism manufacturing method according to the present invention, a spherical base material is press-molded while being heated. A prism body formed into a polygonal column is formed. At least one of a plurality of ridges of the prism body is formed into an R-plane.

In a second prism manufacturing method according to the present invention, a base material in a column shape, each end face of which is projected in a convex form, is press-molded while being heated. A prism body formed into a polygonal column is formed. At least one of a plurality of ridges of the prism body is formed into an R-plane.

EFFECTS OF THE INVENTION

The present invention can provide a prism of which breakage and chipping hardly occur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a main part of an imaging device according to Embodiment 1 of the present invention.

FIG. 2 is a perspective view of a prism according to Embodiment 1.

FIG. 3 is a sectional view showing a construction of a manufacturing apparatus for press-molding a prism.

FIG. 4 shows a base material formed in a column shape of which each end face is projected in a convex form, wherein FIG. 4( a) is a front view and FIG. 4( b) is a side view.

FIG. 5 is a side view of a spherical base material.

FIG. 6 is a diagram showing a configuration of a main part of a lighting device according to Embodiment 2 of the present invention.

EXPLANATION OF THE REFERENCE NUMERALS

-   -   1 imaging device     -   2 lighting device     -   11 light receiving element     -   30 prism     -   31 prism body     -   32 side face     -   32 a light incident plane (orthogonal side face)     -   32 b light exit plane (orthogonal side face)     -   32 c light reflection plane (inclined side face)     -   33 a, 33 b end face     -   35, 36 ridge     -   42 upper die     -   43 lower die     -   44 mold body     -   48 inner space     -   50 base material     -   51 light source

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below with reference to the accompanying drawings.

Embodiment 1

FIG. 1 shows an imaging device 1 according to Embodiment 1 of the present invention. The imaging device 1 includes a light receiving element 11, a plurality of lens groups (specifically, a first lens group 12, a second lens group 13, and a third lens group 14), and a prism 30.

The first lens group 12 is arranged so as to be exposed from the imaging device 1 for receiving external light. The external light made incident from the first lens group 12 is made incident to the prism 30. The incident light is converted by the prism 30 to light different in direction of the optical axis. The converted light is imaged on the light receiving element 11 through the second lens group 13 and the third lens group 14. The imaged image is converted to an electric signal in the light receiving element 11 and is output to be recorded in a recoding section (not shown), such as a memory or the like. The light receiving element 11 may be composed of, for example, a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS), or the like.

The prism 30 includes a prism body 31 formed into a polygonal column (including a truncated pyramid). At least one of a plurality of ridges 35, 36 of the prism body 31 is formed into an R-plane. Accordingly, the ridge 35 or 36 formed into the R-plane is prevented from being broken and chipped.

The prism body 31 in a polygonal column includes a plurality of side faces 32 serving as optical function planes and end faces 33 a, 33 b serving as non-function planes. Each optical function planes herein is a plane having an optical function that transmits and reflects necessary light for actual use thereof while the non-optical function planes is a plane having no optical function. The ridges 35 formed between the side faces 32 and the adjacent end faces 33 a, 33 b are formed into R-planes. Further, the ridges 36 formed between the side faces 32 adjacent to each other are formed into R-planes. Hence, the ridges 35, 36 formed into the R-planes are prevented from being broken and chipped.

In order to secure high optical performance by suppressing breakage and chipping of the prism 30, preferably, all of the plurality of ridges 35, 36 of the prism body 31 are formed into the R-planes.

For example, as shown in FIG. 2, the prism body 31 may be formed into a right triangular prism including orthogonal side faces which are intersected at a right angle with each other and an inclined side face which is inclined with respect to the orthogonal side faces. In the prism body 31, the orthogonal side faces serve as a light incident plane 32 a and a light exit plane 32 b, and the inclined side face serves as a light reflection plane 32 c.

The prism 30 is so formed that light made incident perpendicularly from the light incident plane 32 a is reflected by the light reflection plane 32 c and exits from the light exit plane 32 b. In the imaging device 1, the prism 30 is so arranged that the light incident plane 32 a is located on the first lens group 12 side while the light exit plane 32 b is located on the second lens group 13 side.

In the prism body 31, ridges 35 a, 35 b, 35 c respectively formed between the first end face 33 a and the light incident plane 32 a, the light exit plane 32 b, or the light reflection plane 32 c, which are adjacent to the first end face 33 a, are formed into the R-planes. In the prism body 31, ridges 35 d, 35 e, 35 f respectively formed between the second end face 33 b and the light incident plane 32 a, the light exit plane 32 b, or the light reflection plane 32 c, which are adjacent to the second end face 33 b, are formed into the R-planes. Accordingly, the ridges 35 a to 35 f formed into the R-planes are prevented from being broken and chipped.

Further, in the prism body 31, ridges 36 a, 36 b, 36 c respectively formed between the light incident plane 32 a and the adjacent light exit plane 32 b, between the light exit plane 32 b and the adjacent light reflection plane 32 c, and between the light reflection plane 32 c and the adjacent light incident plane 32 a are formed into the R-planes. Accordingly, the ridges 35, 36 are prevented from being broken and chipped by external impact in conveyance, in mounting to optical equipment, and the like, with a result that the yield of the prism 30 is prevented from lowering and a high-quality prism can be provided.

The material of the prism 30 is not limited especially and may be plastic or glass including cyrstallized glass, for example. A glass material is especially preferable. When the prism 30 is made of glass, high accuracy of form, high thermal resistance, high mechanical durability, and high homogeneity can be achieved. In addition, since glass is comparatively small in thermal expansion coefficient and photoelastic constant, the prism 30 is hardly deformed even if the imaging device 1 is increased in temperature, causing less or no degradation of the optical characteristics of the prism 30.

Moreover, the refractive index of the glass-made prism 30 can be increased comparatively easily. The prism 30 having a high refractive index shortens the length of the optical path of an optical system (the lens groups 12 to 14, the prism 30, and the light receiving element 11) of the imaging device 1. Thus, the imaging device 10 can be compacted.

Increased refractive index of the prism 30 increases the light reflectance of the light reflection plane 32 c. The light reflection plane 32 c is preferable to having 90% or greater light reflectance with respect to visible light (light having a wavelength in the range between 300 nm and 700 nm, both inclusive) made incident perpendicularly to the prism body 31 from the light incident plane 32 a. More preferably, the light reflectance thereof is 95% or greater. For achieving such a high reflectance, the refractive index with respect to the D line (light having a wavelength of 589 nm) of the prism 30 is preferably 1.6 or greater. More preferably, the refractive index thereof is 1.65 or greater. Preferably, the prism 30 has a high transmittance with respect to visible light.

For example, in the case where the prism 30 has a low refractive index (for example, where the prism 30 is made of grass having a low refractive index or plastic), a light reflection film (not shown) may be formed on the light reflection plane 32 c. With the light reflection film formed, the reflectance of the light reflection plane 32 c increases. This achieves high light utilization efficiency. The light reflection film may be made of gold, aluminum, or the like, for example.

FIG. 3 shows a partial sectional view of a manufacturing apparatus 40 of the prism 30. The manufacturing apparatus 40 includes molding dies 41 for press-molding the prism 30. The molding dies 41 include: a pair of an upper die 42 and a lower die 43; and a mold body 44 to which the upper die 42 and the lower die 43 are inserted slidably. The molding faces of the dies, namely, faces forming an internal space 48 to which a base material 50 is inserted are processed into forms having a desired accuracy for molding the optical function planes of the prism 30. For providing high strength to the upper die 42, the lower die 43, and the mold body 44, they are preferably made of hard metal. Alternatively, stainless steel (for example, STAVAX, a product by Uddeholm KK) may be used as the material of the upper die 42, the lower die 43, and the mold body 44. Optionally, a protection film may be formed on the molding faces of the molding dies 41 for enhancing the mold release characteristic of the prism 30 and for suppressing oxidation and corrosion of the molding dies 41. For example, the molding faces may be subjected to electroless nickel plating.

A press head 45 changeable in temperature is mounted at the top of the upper die 42 for vertically moving the upper die 42. The press head 45 includes pressing means 46. A press stage 47 changeable in temperature is mounted at the bottom of the lower die 43.

Description will be given to a method for manufacturing the prism 30 with the use of the above manufacturing apparatus 40.

First, the base material 50 is inserted into the internal space 48 defined and formed by the upper die 42 and the lower die 43 in the mold body 44 of the molding dies 41. The base material 50 is made of glass (K-VC78, a product by Sumita Optical Glass, Inc. or the like), for example. The base material 50 is formed into a column shape of which each end face is projected in a convex shape, as shown in FIG. 4. The base material 50 is inserted so that the column-shaped base material 50 is held at the side face thereof between the upper die 42 and the lower die 43. The base material 50 may be formed into a spherical shape, as shown in FIG. 5.

Subsequently, the upper die 42 and the lower die 43 are heated by the press head 45 and the press stage 47. The heated upper die 42 and the heated lower die 43 heat the base material 50 to a predetermined temperature. For example, the base material 50 is heated up to around the deformation point thereof (around 570° C., for example).

Next, the cylinder 46 is driven to lower the press head 45 to press-mold the base material 50. Press molding is performed in such a manner that the relative positional relationship between the upper die 42 and the lower die 43 is changed to a range satisfying a condition that the volume of the base material 50 is smaller than the volume of the inner space 48 of the molding dies 41 at the time when the press molding is completed.

The heating, is stopped with the relative positional relationship between the upper die 42 and the lower die 43 maintained. Then, the base material 50 is cooled to a temperature around Tg (glass transition point thereof) by the press head 45 and the press stage 47.

Finally, the cylinder 46 is driven to raise the press head 45, and the upper die 42 is taken out from the mold body 44 to open the molding dies 41. Then, the press-molded prism 30 is taken out.

The prism 30 manufactured by the above manufacturing method includes the ridges 35, 36 formed into the R-planes. The ridges 35, 36 are formed into the R-planes simultaneously with formation of the optical function planes and the non-optical function plane, so that brakeage and chipping can be prevented without performing a post treatment, thereby preventing the yield of the prism 30 from lowering.

The light incident plane 32 a and the light exit plane 32 b are intersected at a right angle with each other in Embodiment 1, but may be intersected at any angle.

Further, though the prism 30 in Embodiment 1 is so formed that light made incident from the light incident plane 32 a is reflected by the light reflection plane 32 c and exits from the light exit plane 32 b, the prism 30 may be formed so that light from the first lens group 12 is reflected by an external face as the light reflection plane 32 c and exits on the second lens group 13 side. In other words, the prism 30 is used as a prism of external face reflection type.

Embodiment 2

While Embodiment 1 describes the imaging device 1 using the prism 30, the prism 30 may be used in any optical devices other than the imaging device 1. For example, it may be used in a lighting device. In Embodiment 2, a lighting device 2 including the prism 30 will be descried in detail with reference to FIG. 6. In the description of Embodiment 2, the same reference numerals are assigned to the same constitutional elements as those in FIG. 2 to FIG. 5 for omitting detailed description thereof.

FIG. 6 shows the lighting device 2 according to Embodiment 2 of the present invention. The lighting device 2 according to Embodiment 2 of the present invention includes a light source 51, lens groups (a first lens group 52, a second lens group 53, and a third lens group 54), and the prism 30. In Embodiment 2, the prism 30 is so arranged that the light incident plane 32 a of the prism body 31 is located on the light source 51 side while the light reflection plane 32 c thereof is located on the first lens group 52 side.

The light source 51 is a light source that emits parallel light or diffused light. The light emitted from the light source 51 is transmitted through the first lens group 52 and the second lens group 53 and is made incident to the light incident plane 32 a of the prism 30. The light made incident to the prism 30 is reflected by the light reflection plane 32 c and exits from the light exit plane 32 b. The light exited from the prism 30 is transmitted through the third lens group 54 to be allowed to exit from the lighting device 2.

INDUSTRIAL UTILIZATION

As described above, the present invention is useful for a prism, an imaging device and a lighting device each including it, a prism manufacturing method, and the like. 

1. A prism, comprising: a prism body formed into a polygonal column, wherein at least one of a plurality of ridges of the prism body is formed into an R-plane.
 2. The prism of claim 1, wherein the prism body includes a plurality of side faces and two end faces which form the polygonal column and serve as optical function planes or non-optical function planes, and ridges formed between the respective optical function planes and the respective non-optical function planes, which are adjacent to each other, are formed into R-planes.
 3. The prism of claim 1, wherein the prism body in the polygonal column includes a plurality of side faces serving as optical function planes and two end faces serving as non-optical function planes, and ridges formed between adjacent optical function planes are formed into R-planes.
 4. The prism of claim 1, wherein all of the plurality of ridges are formed into R-planes.
 5. The prism of claim 1, wherein the prism body is in a form of a right triangular prism including two orthogonal side faces which are intersected at a right angle with each other and an inclined side face which is inclined with respect to the two orthogonal side faces.
 6. The prism of claim 5, wherein the inclined side face is provided with a reflection film.
 7. The prism of claim 5, wherein the prism body has a reflectance of 90% or greater at the inclined side face with respect to visible light made incident from one of the two orthogonal side faces perpendicularly to the one orthogonal side face.
 8. The prism of claim 1, wherein the prism body is made of glass.
 9. The prism of claim 1 wherein the prism body has a refractive index of 1.65 or greater with respect to a D line thereof.
 10. An imaging device comprising: a light receiving element; and a prism including a prism body formed into a polygonal column, at least one of a plurality of ridges of the prism body being formed into an R-plane, wherein the prism body is in a form of a right triangular prism including two orthogonal side faces which are intersected at a right angle with each other and an inclined side face which is inclined with respect to the two orthogonal side faces and is arranged so that incident light to the prism body is reflected by the inclined side face toward the light receiving element.
 11. The imaging device of claim 10, wherein the prism body is arranged so that the incident light is made incident from one of the two orthogonal side faces and exits from the other orthogonal side face.
 12. A lighting device, comprising: a light source; and a prism including a prism body formed into a polygonal column, at least one of a plurality of ridges of the prism body being formed into an R-plane, wherein the prism body is in a form of a right triangular prism including two orthogonal side faces which are intersected at a right angle with each other and an inclined side face which is inclined with respect to the two orthogonal side faces and is arranged so that light from the light source is reflected by the inclined side face.
 13. The lighting device of claim 12, wherein the prism is arranged so that light from the light source is made incident from one of the two orthogonal side faces and exits from the other orthogonal side face.
 14. A method for manufacturing a prism including a prism body formed into a polygonal column, at least one of a plurality of ridges of which is formed into an R-plane, comprising the step of: press-molding while heating a spherical base material to obtain the prism.
 15. The prism manufacturing method of claim 14, wherein the press molding step is performed, with the use of a pair of an upper die and a lower die and a mold body to which the upper die and the lower die are inserted slidably, in such a manner that the base material is inserted into an inner space defined and formed between the upper die and the lower die in the mold body and a relative positional relationship between the upper die and the lower die is changed to a range satisfying a condition that a volume of the base material is smaller than a volume of the inner space at a time when the press molding is completed.
 16. A method for manufacturing a prism including a prism body formed into a polygonal column, at least one of a plurality of ridges of which is formed into an R-plane, comprising the step of press-molding while heating a base material in a column shape, each end face of which is projected in a convex form, to obtain the prism.
 17. The prism manufacturing method of claim 16, wherein the press molding step is performed, with the use of a pair of an upper die and a lower die and a mold body to which the upper die and the lower die are inserted slidably, in such a manner that the base material is inserted into an inner space defined and formed between the upper die and the lower die in the mold body and a relative positional relationship between the upper die and the lower die is changed to a range satisfying a condition that a volume of the base material is smaller than a volume of the inner space at a time when the press molding is completed. 